Velocity modulated beam tubes with reflector electrodes



Oct. 9, 1951 E. TouRAToN ET AL 2,570,289

VELOCITY MODULATED BEAM TUBES WITH REFLECTOR ELEcTRoDEs Filed April 29, 1947 Patented Oct. 9, 1,951

VELOCITY MODULATED BEAM TUBES WITH REFLECTOR ELECTRODES Emile Touraton, Ren Zwobada, and Anne Marie Gratzmuller, Paris, France, assignors to International Standard Electric Corporation, New

York, N. Y.

Application April 29, 1947, Serial No. 744,690 In France April 12, 1946 section 1, Public Law 69o, August s, 1946l 4 Patent expires April 12, 1966 (Cl. S15- 39) 2 Claims.

E The present invention relates to a velocity modulation tube which may be used as oscillator or amplifier.

One object of the invention is an increase of Vthe output power or a widening the bandwidth by means of a device for transferring energy of the electron beam.

According to one feature of the invention the `:modulated beam travels twice in the catcher gap,

a `first time in the normal direction and a second time after it has been reflected in a decelerating field.

According to another feature, the beam is slowed down or decelerated at its second passage and the electrons are collected at a low potential by one or more electrodes conveniently located.

According to another feature of the invention the electron beam is flattened for an easier separation of the forward and backward beams.

According to another feature of the invention the transit time and distance travelled by one electron, between its two passages in the catcher gap are such that their effect is cumulative. Other features and characteristics of the invention will be apparent from the following description of an embodiment described in relation with the drawing in which:

The only figure shows a velocity modulated tube incorporating features of the invention.

Referring to the figure. the embodiment de scribed comprises a cathode I, a grid or Wehnelt electrode 2, a first cavity resonator 3 comprising a modulating gap 1I, a decelerating electrode 5, a cavity resonator a catcher gap 'I and three electrodes 8, 9 and I0.

The electrode I is of annular shape and the electron beam is in the form of a hollow cylinder. The electrode 2 is brought to a negative potential with respect to the cathode. The beam is accelerated by the potential Uu of the resonator 3, and converges in gap 4 where it is modulated, it then diverges and is decelerated by electrode 5 which is brought to a negative potential Uc. The beam converges again, is accelerated and focalised in the catcher gap 1, where it gives up for the rst time part of its high frequency energy. It diverges in the decelerating field created by electrode 8 brought to a negative potential -U0 with respect to the cathode and is reflected; the beam then converges again in gap` I and diverges in the canal space between the resonator E and electrode 9. The electrons are collected by electrode ID brought to potential U'o. The shape of electrodes 5, 9 and I0 and resonator 6 are such that the electron beam is reflected without appreciable change in shape. II and I2 are respectively the input and output loops. f

On the drawing, the path of the elec'tronsis shown in dotted lines. It is possible to estimate approximately the increase in eiciency or the widening of the band width as follows: The electron beam is equivalent to a current of mean intensity in Where (i) is the amplitude of the fundamental frequency f. When it flows through a catcher gap whose impedance is where Q is the power loss factor, w=21rf and C the capacity, the band width is f AfQ and the energy is proportional to R12.

The same electron beam flows twice through the catcher gap. The amplitude of the fundamental frequency being constant and equal to i the transit time between the two passages being an odd multiple of a half period, the result is the same as if the cavity resonator was excited by two modulated opposite current components but 1/2 period out of phase. It follows that the D. C. component will be zero and that the amplitude of the first harmonic will be doubled.

Therefore, if the cavity resonator is tuned on this first harmonic the power will be increased fourfold.

In the example considered of a velocity modulation tube the amplitude of the fundamental frequency of the modulated beam is not constant but proportional to Bessel function J1 (Ka), where (a) is the distance travelled by the beam, K a constant of value depending on the frequency and the potential applied in the normal operation of the tube. This amplitude is proportional to the first maximum of function J1 for the first passage in the catcher gap and since the various maxima of J1 are not equa-1 the power delivered to the cavity resonator tuned on the rst harmonic is not multiplied exactly by 4 but by a factor depending on the amplitude of the maxima.

It is possible not to use two maxima but a positive maximum and a negative minimum of function J1. In this case the transit time between the two successive passages of the beam in the catcher gap must be an even multiple of a halfperiod.

In an embodiment of the invention the beam flows twice in the catcher gap with an appropriate 'phase `so that the cavity resonator be excited at each half period and the result is the same as if the cavity resonator was excited by twov modulated currents.

If it is assumed that the average return speed,

is the same as the average speed in the normal direction the mean current zero.. It maybe assured also that the fundamentalY component of the modulated current is proportional to the rst maximum of the Bessel J 1V (in) function for the for-ward travel and to the second maximum of the same function for the `backward travel of the beam as described in an article by A. E. Harrison published in Proceedings of the' Institute of Radio Engineers, vol. 33, No. 1f, Jan

uary 1945. It must be notedrthat the. second maximum to be considered is algebraically the' iirst minimum.

We claim: Y

.1. An electron discharge device of the velocity `modulation* type comprisingan annular electron lfor producing a hollow. cylindrical beam of electrons, a focusing electrode arranged about said gunfor` focusing said. beam' into a point, a

beam, and a reflector and focusing electrode mounted adjacent said second resonator to reflect said beam through said second resonator with a point of focus at'the gap therein and in a path different from that of the beam in its first passage through said second resonator, said reflecting `electrode being provided with side walls adjacentsaidfbeam path and a central extension for dilating said hollow beam.

2. An electron discharge device according to claim lfurther comprising a collector electrode mounted adjacent said drift space means for collecting the reflected electrons from the hollow dilated beam.

EMILE TOURATON. REN ZWOBADA. ANNE MARIE GRATZMULLER.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS 

